Voltage surges can be a threat to electronic circuitry, especially in components and systems where continuous functioning is necessary. For example, in an electronically controlled building access system, it is necessary that the system functions continuously to prevent people from being trapped inside the building or locked out of the building in the event of an emergency. Thus, it is important that the electronic equipment used in such systems has protection to prevent the effects of transient voltages. This protection may be achieved by including specialized circuitry within the electronic equipment or by adding transient voltage suppression devices within the system.
With the introduction of Power over Ethernet (PoE), devices such as telephones, door access readers, door sensors, cameras, and wireless access points are being powered using Ethernet network cabling. In the past, separate 120V cabling had to be installed along with communications cabling in order to power and communicate with these types of devices. PoE eliminates the need to run additional power cabling by injecting a DC voltage onto an Ethernet network.
A DC voltage can be injected on Ethernet cabling by using a network switch with PoE capabilities or a PoE injector device. Usually, a PoE injector is used if a network is already installed in a building because it may be costly to change an existing non-PoE switch to a PoE switch. Either device is installed in a network closet or a telecommunications room.
The need for transient voltage suppression on data lines using PoE is driven by the increasing number of Ethernet users wanting to take advantage of the convenience and the cost savings that PoE offers. Additionally, safety standards require transient voltage suppression in this area. For example, Underwriter's Laboratory (UL) published an access system standard under UL 294 titled “Access Control System Units.” One aspect of this specification is that listed components are capable of suppressing a transient voltage surge of 2400V/12A on output circuitry.
Local authorities may require access control systems to be UL listed, and for a system to be UL listed, it is important for every component in the system to be UL listed (i.e. power supply, door controller, card reader, etc.).
In the prior art, PoE switches and PoE injector devices are not known to handle the transient voltages stated in UL specifications. Therefore, it would be desirable to provide a device to PoE systems that will accomplish transient voltage suppression and protect the PoE power source.